1. Technical Field
This invention is related to the field of internal combustion (IC) engine ignition diganosis systems. More particularly, it is related to the field of detecting ionization current in the combustion chamber of IC engines and using the detected ionization signal to monitor ignition parameters and diagnose engine performance.
2. Discussion
The prior art includes a variety of conventional methods for detecting and using ionization current in a combustion chamber of an internal combustion engine. However, each of the various conventional systems suffer from a great variety of deficiencies. For example, prior art ionization current detection circuits are generally too slow and generate a current signal with low signal-to-noise ratio.
The ionization current of an internal combustion engine can be used for diagnosing engine misfire, knock, ignition timing and duration, etc. Through sophisticated signal conditioning processing, the individual cylinder combustion properties can also be obtained. Therefore, the engine combustion process can be precisely monitored and controlled in closed loop. To detect in-cylinder ions generated during the combustion process, a DC bias voltage needs to be applied between the spark plug gap. There are two ways to generate the DC bias: conventional DC power supply (large electronics) and capacitor charges by primary or secondary flyback voltage (high voltage capacitor). Both approaches present disadvantages due to the size of DC power supply and reliability of high voltage capacitors.